Fix Pool not raising an error when no package could be found

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed permission errors when adding/removing git dependencies on Windows.
+- Fixed `Pool` not raising an exception when no package could be found.
 
 
 ## [0.12.7] - 2018-11-08

poetry/repositories/pool.py

@@ -73,7 +73,7 @@ class Pool(BaseRepository):
 
                 return package
 
-        return None
+        raise PackageNotFound("Package {} ({}) not found.".format(name, version))
 
     def find_packages(
         self, name, constraint=None, extras=None, allow_prereleases=False

tests/repositories/test_pool.py

+import pytest
+
+from poetry.repositories import Pool
+from poetry.repositories import Repository
+from poetry.repositories.exceptions import PackageNotFound
+
+
+def test_pool_raises_package_not_found_when_no_package_is_found():
+    pool = Pool()
+    pool.add_repository(Repository())
+
+    with pytest.raises(PackageNotFound):
+        pool.package("foo", "1.0.0")